Interference measurements and channel state information feedback for multi-user multiple-in multiple-out

ABSTRACT

Methods and apparatuses for channel state information (CSI) feedback in a wireless network. In one embodiment, a method includes receiving signaling including a first Non-Zero Power (NZP) CSI-reference signal (RS) configuration for channel measurement; a second NZP CSI-RS configuration; and a CSI interference measurement (CSI-IM) configuration for interference measurement. The method includes receiving a CSI feedback request and estimating the CSI based on at least the signaled first NZP CSI-RS configuration, the second NZP CSI-RS configuration, and the CSI-IM configuration.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority toInternational Application No. PCT/IB2018/053133, filed May 4, 2018,entitled “INTERFERENCE MEASUREMENTS AND CHANNEL STATE INFORMATIONFEEDBACK FOR MULTI-USER MULTIPLE-IN MULTIPLE-OUT,” which claims priorityto U.S. Provisional Application No. 62/502,454, filed May 5, 2017entitled “INTERFERENCE MEASUREMENTS AND CSI FEEDBACK FOR MU-MIMO,” theentireties of both of which are incorporated herein by reference.

TECHNICAL FIELD

Wireless communication and in particular, to interference measurementsfor multi-user multiple-in multiple-output (MU-MIMO) devices.

BACKGROUND

The next generation mobile wireless communication system (5G) or newradio (NR), may support a diverse set of use cases and a diverse set ofdeployment scenarios. The later includes deployment at both lowfrequencies (100 s of MHz), similar to existing (Long Term Evolution)LTE systems, and very high frequencies (e.g., mm waves in the tens ofGHz). Similar to LTE, NR may use Orthogonal Frequency DivisionMultiplexing (OFDM) in the downlink (i.e., from a network node, gNB,eNB, or base station (BS), to a wireless device (WD)). In the uplink(i.e., from wireless device to network node), both OFDM and DiscreteFourier Transform (DFT)-spread OFDM (DFT-S-OFDM), also known assingle-carrier frequency division multiple access (SC-FDMA) in LTE, maybe supported.

The basic NR physical resource can be seen as a time-frequency gridsimilar to the grid in LTE as illustrated in FIG. 1, which is a blockdiagram of LTE physical resources, where each resource elementcorresponds to one OFDM subcarrier during one OFDM symbol interval.Although a subcarrier spacing of Δf 15 kHz is shown in FIG. 1, differentsubcarrier spacing values are supported in NR. The supported subcarrierspacing values (also referred to as different numerologies) in NR aregiven by Δf (15×2^(α)) kHz where a is a non-negative integer.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks (RBs), where a resource block corresponds toone slot (0.5 ms) in the time domain and twelve contiguous subcarriersin the frequency domain. Resource blocks are numbered in the frequencydomain, starting with 0 from one end of the system bandwidth. For NR,resource allocation is described in terms of resource blocks infrequency domain and OFDM symbols in time domain. A resource block in NRmay also be twelve subcarriers in frequency. A RB is also referred to asphysical RB (PRB) herein. In the time domain, downlink and uplinktransmissions in NR may be organized into equally-sized subframessimilar to LTE as shown in FIG. 2, which is a block diagram of the LTEtime-domain structure with 15 kHz subcarrier spacing. In NR, a subframemay be further divided into multiple slots of equal duration. Datascheduling in NR can be either on a subframe basis as in LTE, or on aslot basis. In NR, subframe length may be fixed at 1 ms regardless ofthe numerology used. In NR, the slot duration for a numerology of(15×2^(α))kHz may be given by ½^(α) ms assuming 14 OFDM symbols perslot, and the number of slots per subframe depends on the numerology.For convenience, subframe is used herein.

Downlink transmissions are dynamically scheduled, i.e., in each subframethe gNB transmits downlink control information (DCI) about which data isto be transmitted to and which resource blocks in the current downlinksubframe the data is transmitted on. This control signaling is typicallytransmitted in the first one or two OFDM symbols in each subframe in NR.The control information may be carried on Physical Downlink ControlChannel (PDCCH) and data may be carried on Physical Downlink SharedChannel (PDSCH). A wireless device first detects and decodes PDCCH andif a PDCCH is decoded successfully, the wireless device decodes thecorresponding PDSCH based on the decoded control information in thePDCCH.

Uplink data transmissions may also be dynamically scheduled using PDCCH.Similar to downlink, a wireless device first decodes uplink grants inPDCCH and then transmits data over the Physical Uplink Shared Channel(PUSCH) based the decoded control information in the uplink grant suchas modulation order, coding rate, uplink resource allocation, and etc.

Spatial Multiplexing

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance may bein particular improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO. A core component inLTE and NR is the support of MIMO antenna deployments and MIMO relatedtechniques. Spatial multiplexing is one of the MIMO techniques used toachieve high data rates in favorable channel conditions. An illustrationof the spatial multiplexing operation is provided in FIG. 3, whichillustrates an exemplary transmission structure of precoded spatialmultiplexing mode in LTE.

As seen in FIG. 3, the information carrying symbol vector s≤[s₁, s₂, . .. , s_(r)]^(T) is multiplied by an N_(T)×r precoder matrix W, whichserves to distribute the transmit energy in a subspace of the N_(T)(corresponding to N_(T) antenna ports) dimensional vector space. Theprecoder matrix is typically selected from a codebook of possibleprecoder matrices, and typically indicated by means of a precoder matrixindicator (PMI), which specifies a unique precoder matrix in thecodebook for a given number of symbol streams. Each symbol in s [s₁, s₂,. . . , s_(r)]^(T)corresponds to a MIMO layer and r may be referred toas the transmission rank. In this way, spatial multiplexing may beachieved since multiple symbols can be transmitted simultaneously overthe same time/frequency resource element (RE). The number of symbols ris typically adapted to suit the current channel properties.

The received signal at a UE with N_(R) receive antennas at a certain REn is given by

y _(n) H _(n) Ws+e _(n)

where y_(n) is a N_(R)×1 received signal vector, H_(n) a N_(R)×N_(T)channel matrix at the RE, e_(n) is a N_(R)×1 noise and interferencevector received at the RE by the UE. The precoder W can be a widebandprecoder, which is constant over frequency, or frequency selective,i.e., different over frequency. The precoder matrix is often chosen tomatch the characteristics of the N_(R)×N_(T) MIMO channel matrix H_(n),resulting in so-called channel dependent precoding. This is alsocommonly referred to as closed-loop precoding and essentially strivesfor focusing the transmit energy into a subspace which is strong in thesense of conveying much of the transmitted energy to the wirelessdevice. In addition, the precoder matrix may also be selected to strivefor orthogonalizing the channel, meaning that after proper linearequalization at the wireless device, the inter-layer interference may bereduced.

The transmission rank, and thus the number of spatially multiplexedlayers, is reflected in the number of columns of the precoder. Thetransmission rank may also be dependent on the Signal to Noise plusInterference Ratio (SINR) observed at the wireless device. Typically, ahigher SINR is required for transmissions with higher ranks. Forefficient performance, it may be important that a transmission rank thatmatches the channel properties as well as the interference is selected.

Channel State Information Reference Signals (CSI-RS)

In LTE, CSI-RS was introduced for channel estimations in the downlinkfor transmission modes 9 and 10. A unique CSI-RS may be allocated toeach network node transmit antenna (or antenna port) and may be used bya UE to measure downlink channel associated with each of transmitantenna ports. CSI reference signals are defined for one to 32 antennaports. The antenna ports sometimes are also referred to as CSI-RS ports.CSI-RS are transmitted in certain REs and subframes. FIG. 4 is a blockdiagram of REs available for CSI-RS allocation in each PRB in LTE. FIG.4 shows the REs available for CSI-RS allocations in each PRB in LTE. Upto 40 REs can be configured for CSI-RS.

For two antenna ports, a CSI-RS for each antenna port may be allocatedwith two REs in the same subcarrrier and in two adjacent OFDM symbols ineach PRB. CSI-RS signals for two antenna ports are multiplexed using alength two orthogonal cover codes (OCC), also referred to as OCC2. Thus,for 2 antenna ports, there are 20 different patterns available within asubframe. FIGS. 5 and 6 show an example of CSI-RS resource for 2 and 4ports in LTE, respectively.

By measuring CSI-RS, a wireless device can estimate the channel theCSI-RS is traversing including the radio propagation channel and antennagains. This type of CSI-RS may also be referred to as Non-Zero Power(NZP) CSI-RS. In addition to NZP CSI-RS, Zero Power (ZP) CSI-RS wasintroduced in LTE. ZP CSI-RS may be defined on one or more 4-port CSI-RSresource. The purpose was to indicate to a wireless device that theassociated REs are muted at the network node. If the ZP CSI-RS may beallocated to be fully overlapping with NZP CSI-RS in an adjacent cell toimprove channel estimation by wireless devices in the adjacent cellsince there is no interference created by this cell. An example ofZP-CSI-RS resource is shown in FIG. 7, where the ZP CSI-RS occupies 8REs per PRB (i.e., two 4-port CSI-RS resources). FIG. 7 is therefore ablock diagram of NZP CSI-RS and ZP CSI-RS.

In LTE release (Rel) 11, CSI interference measurement (CSI-IM) resourcewas also introduced for a wireless device to measure interference. ACSI-IM resource may be defined as a 4-port CSI-RS resource that may bealso fully overlapped with ZP CSI-RS. A CSI process may be defined by aNZP CSI-RS resource for channel estimation and an CSI-IM resource forinterference and noise estimation. A wireless device can estimate theeffective channel and noise plus interference for a CSI-RS process andconsequently determine the rank, precoding matrix, and the channelquality. FIG. 8 is a block diagram of NZP CSI-RS, ZP CSI-RS and CSI-IM.

CSI Feedback

For CSI feedback, LTE has adopted an implicit CSI mechanism where awireless device feedback of the downlink channel state information is interms of a transmission rank indicator (RI), a precoder matrix indicator(PMI), and one or two channel quality indicator(s) (CQI). The CQI/RI/PMIreport can be wideband or frequency selective depending on whichreporting mode that is configured. The RI corresponds to a recommendednumber of layers that are to be spatially multiplexed and thustransmitted in parallel over the effective channel. The PMI identifies arecommended precoder. The CQI represents a recommended modulation level(i.e., QPSK, 16QAM, etc.) and coding rate for each transport block. LTEsupports transmission of one or two transport blocks (i.e., separatelyencoded blocks of information) to a wireless device in a subframe. Thereis thus a relation between a CQI and an SINR of the spatial layers overwhich the transport block or blocks are transmitted.

Beamformed CSI-RS

The beamformed (or precoded) CSI-RS concept was introduced in LTE, inwhich a CSI-RS is precoded and transmitted over more than one antennaport. This is in contrast with non-precoded CSI-RS in which each CSI-RSis transmitted on one antenna port. Beamformed CSI-RS can be used whenthe direction of a wireless device or wireless devices is roughly knownso that CSI-RS can be transmitted in a narrow beam or beams to reach thewireless device or wireless devices. This can improve CSI-RS coveragewith increased beamforming gain and also reduce CSI-RS resource and CSIfeedback overhead.

The non-precoded CSI-RS based feedback is referred as “CLASS A” CSIfeedback, while beamformed CSI-RS operation is referred to as “Class B”CSI feedback. In CLASS B CSI feedback, a wireless device can beconfigured with up to 8 CSI-RS resources (i.e., multiple CSI-RS beams),each with up to 8 ports. The wireless device reports back a CSI-RSresource indicator (CRI) to indicate the best beam and the correspondingCQI, RI, PMI within the selected beam.

A wireless device configured for Class B operation with one CSI-RSresource of up to 8 ports is a special case, in which each CSI-RS portmay correspond to a particular beam. In that case, a wireless device maybe configured to use a port selection and combining codebook.

Hybrid Class A and Class B CSI reporting may also be supported. In onescenario, Class A is used to identify the approximate direction of awireless device while Class B is used to “fine tune” the CSI.

MU-MIMO

When all the data layers are transmitted to one wireless device, it maybe referred to as single user multiple-in multiple-output or SU-MIMO. Onthe other hand, when the data layers are transmitted to multiplewireless devices, it may be referred to as multi-user MIMO or MU-MIMO.MU-MIMO is possible when, for example, two wireless devices are locatedin different areas of a cell such that they can be separated throughdifferent precoders (or beams) at the network node, e.g., eNB/gNB. Thetwo wireless devices may be served on the same time-frequency resources(e.g., PRBs) by using different precoders or beams. MU-MIMO may requiremuch more accurate downlink channel information than in SU-MIMO in orderfor the network node to use precoding to separate the wireless devices,i.e., reducing cross interference to the co-scheduled wireless devices.For that purpose, advanced CSI feedback was introduced in LTE in which anew codebook was defined trying to capture more accurate downlinkchannel information. In NR, a type II codebook may be designed for thesame purpose.

MU-MIMO Interference

In MU-MIMO, in addition to interference from other cells, also referredto as inter-cell interference, interference among UEs participating inMU-MIMO may also be experienced by the wireless devices, also referredto as intra-cell interference or MU interference. MU interference may bemore difficult to measure or estimate due to the dynamic nature oftransmissions to wireless devices paired in MU-MIMO. Assuming there areK+1 wireless devices sharing the same time-frequency resources in a datatransmission, the received signal at the kth (k1, 2, . . . ,K+1)wireless device and at the ith RE can be expressed as

y ^(k)(i)=H ^(k)(i)W ^(k)(i)s ^(k)(i)+H ^(k)(i)Σ_(m≠k) ^(K+1) W ^(m)(i)s^(m)(i)+e ^(k)(i)

where H^(k)(i), W^(k)(i), s^(k)(i) are the channel matrix, the precodingmatrix and the data vector associated with the kth wireless device atthe ith RE. MU interference experienced at the kth wireless device maybe expressed as

I _(MU) ^(k) =H ^(k)(i)Σ_(m≠k) ^(K+1) W _(m)(i)s ^(m)(i)

and e^(k)(i) may be the noise plus inter-cell interference received atthe kth wireless device. Only e^(k)(i) is typically considered in theexisting LTE CSI feedback. Existing CSI reporting defined in LTE ismainly for SU-MIMO operation, in which a wireless device is configuredwith one CSI-RS resource for channel measurement and one CSI-IM resourcefor interference measurement. With the number of supported antenna portsincreasing in both LTE and NR, supporting MU-MIMO becomes even moreimportant. Existing CSI feedback in LTE may not be sufficient to supportMU-MIMO. Theoretically, ZP-CSI-RS can be used by eNB/gNB to emulateMU-MIMO interference by injecting MU interference in the ZP CSI-RSresource. However, a separate ZP CSI-RS may be generally needed for eachwireless device and when many wireless devices are participatingMU-MIMO, the required ZP CSI-RS resources can be large. Unfortunately,this may significantly increase the overhead of ZP CSI-RS.

SUMMARY

Some embodiments advantageously provide methods and apparatuses forinterference measurements and CSI feedback for MU-MIMO.

According to a first method/process:

-   -   1. The network node first obtains SU-MIMO CSI from serving        wireless devices as is normally done in LTE or NR, and        determines K+1 (K>0) wireless device candidates for MU-MIMO.    -   2. The network node configures each of the K+1 wireless device        candidates with K+1 NZP CSI-RS resources and one common ZP        CSI-RS as CSI-IM in the same subframe or slot and request CSI        report from each wireless device. The network node may also        configure an Energy Per RE (EPRE) power ratio,

${\beta = \frac{{EPRE}_{PDSCH}}{{EPRE}_{{{NZP}\mspace{14mu} {CSI}} - {RS}}}},$

between PDSCH and NZP CSI-RS for each of the K+1 NZP CSI-RS.

-   -   3. For each wireless device, the network node also indicates one        of the K+1 NZP CSI-RS resources for channel measurement and the        remaining K NZP CSI-RS for interference measurements. Each        wireless device is also configured with a codebook for CSI        feedback.    -   4. Each wireless device measures inter-cell interference,        I_(inter-cell), over the ZP-CSI-RS resource, and MU-MIMO        interference, I_(m) (m=1, . . . K), on each of the K NZP CSI-RS        resources configured for interference measurement by assuming        isotropical interference, i.e., power averaging over all ports        in a CSI-RS resource.    -   5. Each wireless device estimates the total interference as        I=Σ₌₁ ^(K)(I_(m)−I_(inter-cell))+I_(inter-cell) and calculates        CSI according to the configured codebook.

According to a second method/process:

-   -   1. Similar to the first step in the first method (method 1)        above, i.e., Network node first obtains SU-MIMO CSI from serving        wireless devices as is normally done in LTE or NR, and        determines K+1 wireless device candidates for MU-MIMO.    -   2. The network node configures each of the K+1 (K>0) wireless        device candidates with one NZP CSI-RS resource and one ZP        CSI-RS. The ZP CSI-RS is common to the K+1 wireless devices in        the same subframe or slot and request CSI report from each        wireless device. In one or more embodiments, the network node        also signals an Energy Per RE (EPRE) power ratio,

${\beta = \frac{{EPRE}_{PDSCH}}{{EPRE}_{{{NZP}\mspace{14mu} {CSI}} - {RS}}}},$

between PDSCH and the NZP CSI-RS.

-   -   3. The network node transmits a signal representing a MU-MIMO        signal for all of the K+1 wireless devices in the ZP CSI-RS        resource, i.e., transmitting signal Σ_(k=1) ^(K+1)W^(k)s^(k) on        the ZP CSI-RS resource, where W^(k) and s^(k) are the procoding        matrix and signal associated with the kth wireless device.    -   4. Each wireless device measures interference, I_(ZP), over the        ZP-CSI-RS resource and estimates a precoded signal power,        p_(s)=β·∥HW∥Λ2, over the NZP CSI-RS resource, where H is the        estimated channel matrix and W is the estimated precoding matrix        based channel estimation on the NZP CSI-RS resource configured        for channel estimation.    -   5. Each wireless device calculates CSI by assuming I        =I_(ZP)−p_(s) as the total interference and channel estimation H        according to the configured codebook.

According to one aspect of the disclosure, a method for a UE isprovided. The method includes receiving signaling, by the UE, thesignaling including: a first Non-Zero Power (NZP) channel stateinformation-reference signal (CSI-RS) configuration for channelmeasurement; a second NZP CSI-RS configuration for interferencemeasurement; and a CSI interference measurement (CSI-IM) configurationfor interference measurement; and estimating, by the UE, CSI based atleast in part on the signaled first NZP CSI-RS configuration, the secondNZP CSI-RS configuration, and the CSI-IM configuration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments, the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the receiving signalingfurther includes receiving the signaling including a codebookconfiguration. In some embodiments, the estimating the CSI furthercomprises estimating the CSI based on the codebook configuration. Insome embodiments, the method further comprises receiving, by the UE, aCSI feedback request for CSI based on at least the first NZP CSI-RSconfiguration, the second NZP CSI-RS configuration, the CSI-IMconfiguration and the codebook configuration. In some embodiments, themethod further comprises receiving, by the UE, a CSI feedback requestfor CSI based on at least the first NZP CSI-RS configuration, the secondNZP CSI-RS configuration, and the CSI-IM configuration. In someembodiments, the estimating the CSI further includes measuring adownlink channel on a first NZP CSI-RS resource corresponding to thefirst NZP CSI-RS configuration. In some embodiments, the estimating theCSI further includes measuring interference on each of K NZP CSI-RSresources corresponding to the second NZP CSI-RS configuration. In someembodiments, the measuring the interference on each of the K NZP CSI-RSresources results in K interference power estimates. In someembodiments, each of the K interference power estimates is scaledaccording to a power scaling factor associated with the K NZP CSI-RSresources. In some embodiments, the second NZP CSI-RS configurationcomprises a power scaling factor for each of K NZP CSI-RS resourcesconfigured by the second NZP CSI-RS configuration for the interferencemeasurement. In some embodiments, the estimating the CSI includesmeasuring interference on at least one CSI-IM resource corresponding tothe CSI-IM configuration. In some embodiments, the measuring theinterference on the at least one CSI-IM resource results in at least oneinterference power estimate. In some embodiments, the method furthercomprises adding at least the K interference power estimates based onthe K NZP CSI-RS resources and the at least one interference powerestimate based on the at least one CSI-IM resource to obtain a combinedinterference estimate. In some embodiments, the estimated CSI is basedon the combined interference estimate and a measured downlink channel.In some embodiments, the measured downlink channel is measured on afirst NZP CSI-RS resource corresponding to the first NZP CSI-RSconfiguration. In some embodiments, the method further comprisesreceiving, by the UE, a CSI feedback request comprising a codebookconfiguration.

According to another aspect of the disclosure, a UE comprisingprocessing circuitry is provided. The processing circuitry is configuredto cause the UE to: receive signaling, the signaling including: a firstNon-Zero Power (NZP) channel state information (CSI)-reference signal(RS) configuration for channel measurement; a second NZP CSI-RSconfiguration for interference measurement; and a CSI interferencemeasurement (CSI-IM) configuration for interference measurement; andestimate CSI based at least in part on the signaled first NZP CSI-RSconfiguration, the second NZP CSI-RS configuration, and the CSI-IMconfiguration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments, the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the received signalingfurther includes a codebook configuration. In some embodiments, theprocessing circuitry is configured to cause the UE to estimate the CSIby being further configured to estimate the CSI based on the codebookconfiguration. In some embodiments, the processing circuitry is furtherconfigured to cause the UE to receive a CSI feedback request for CSIbased on at least the first NZP CSI-RS configuration, the second NZPCSI-RS configuration, the CSI-IM configuration and the codebookconfiguration. In some embodiments, the processing circuitry is furtherconfigured to cause the UE to receive a CSI feedback request for CSIbased on at least the first NZP CSI-RS configuration, the second NZPCSI-RS configuration, and the CSI-IM configuration. In some embodiments,the processing circuitry is configured to cause the UE to estimate theCSI by being further configured to measure a downlink channel on a firstNZP CSI-RS resource corresponding to the first NZP CSI-RS configuration.In some embodiments, the processing circuitry is configured to cause theUE to estimate the CSI by being further configured to measureinterference on each of K NZP CSI-RS resources corresponding to thesecond NZP CSI-RS configuration. In some embodiments, the processingcircuitry is configured to measure the interference on each of the K NZPCSI-RS resources resulting in K interference power estimates. In someembodiments, the processing circuitry is configured to scale each of theK interference power estimates according to a power scaling factorassociated with the K NZP CSI-RS resources. In some embodiments, thesecond NZP CSI-RS configuration comprises a power scaling factor foreach of K NZP CSI-RS resources configured by the second NZP CSI-RSconfiguration for the interference measurement. In some embodiments, theprocessing circuitry is configured to cause the UE to estimate the CSIby being further configured to measure interference on at least oneCSI-IM resource corresponding to the CSI-IM configuration. In someembodiments, the processing circuitry is configured to measure theinterference on the at least one CSI-IM resource resulting in at leastone interference power estimate. In some embodiments, the processingcircuitry is configured to cause the UE to add at least the Kinterference power estimates based on the K NZP CSI-RS resources and theat least one interference power estimate based on the at least oneCSI-IM resource to obtain a combined interference estimate. In someembodiments, the processing circuitry is configured to cause the UE toestimate the CSI based on the combined interference estimate and ameasured downlink channel. In some embodiments, the measured downlinkchannel is measured on a first NZP CSI-RS resource corresponding to thefirst NZP CSI-RS configuration. In some embodiments, the processingcircuitry is further configured to cause the UE to receive a CSIfeedback request comprising a codebook configuration.

According to yet another aspect of the disclosure, a method for a basestation is provided. The method includes signaling, by the base station,to a user equipment, UE: a first Non-Zero Power (NZP) channel stateinformation (CSI)-reference signal (RS) configuration for channelmeasurement; a second NZP CSI-RS configuration for interferencemeasurement; and a CSI interference measurement (CSI-IM) configurationfor interference measurement; and receiving, by the base station, a CSIreport from the UE, the CSI report being based at least in part on thesignaled first NZP CSI-RS configuration, the second NZP CSI-RSconfiguration, and the CSI-IM configuration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments, the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the signaling furtherincludes signaling a codebook configuration. In some embodiments, thereceived CSI report is based at least in part on the signaled codebookconfiguration. In some embodiments, the method further includes sending,from the base station, a CSI feedback request to the UE for CSI based onat least the first NZP CSI-RS configuration, the second NZP CSI-RSconfiguration, the CSI-IM configuration, and the codebook configuration.In some embodiments, the method further includes sending, from the basestation, a CSI feedback request to the UE for CSI based on at least thefirst NZP CSI-RS configuration, the second NZP CSI-RS configuration andthe CSI-IM configuration. In some embodiments, the method furtherincludes transmitting, from the base station, K+1 NZP CSI-referencesignals (RSs) over K+1 NZP CSI-RS resources configured by the signalingof the first NZP CSI-RS configuration and the second NZP CSI-RSconfiguration. In some embodiments, the signaling, by the base station,to the UE includes signaling semi-statically over radio resource controlsignaling. In some embodiments, the sending, from the base station, theCSI feedback request to the UE includes sending the CSI feedback requestdynamically over a downlink control channel. In some embodiments, thesecond NZP CSI-RS configuration comprises a power scaling factor foreach of K NZP CSI-RS resources configured by the second NZP CSI-RSconfiguration for the interference measurement. In some embodiments, thereceived CSI report is based on a combined interference estimate and ameasured downlink channel, the combined interference estimate being asum of at least K interference power estimates based on K NZP CSI-RSresources configured by the second NZP CSI-RS configuration and at leastone interference power estimate based on at least one CSI-IM resourceconfigured by the CSI-IM configuration, and the measured downlinkchannel being based on a first NZP CSI-RS resource corresponding to thefirst NZP CSI-RS configuration. In some embodiments, the method furtherincludes sending, from the base station, a CSI feedback requestcomprising a codebook configuration.

According to yet another aspect of the disclosure, a base stationcomprising processing circuitry is provided. The processing circuitry isconfigured to cause the base station to: signal to a UE: a firstNon-Zero Power (NZP) channel state information (CSI)-reference signal(RS) configuration for channel measurement; a second NZP CSI-RSconfiguration for interference measurement; and a CSI interferencemeasurement (CSI-IM) configuration for interference measurement; andreceive a CSI report from the UE, the CSI report being based at least inpart on the signaled first NZP CSI-RS configuration, the second NZPCSI-RS configuration, and the CSI-IM configuration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments) the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the processing circuitryis configured to signal to the UE by being further configured to signala codebook configuration. In some embodiments, the received CSI reportis based at least in part on the signaled codebook configuration. Insome embodiments, the processing circuitry is further configured to senda CSI feedback request to the UE for CSI based on at least the first NZPCSI-RS configuration, the second NZP CSI-RS configuration, the CSI-IMconfiguration, and the codebook configuration. In some embodiments, theprocessing circuitry is further configured to send a CSI feedbackrequest to the UE for CSI based on at least the first NZP CSI-RSconfiguration, the second NZP CSI-RS configuration and the CSI-IMconfiguration. In some embodiments, the processing circuitry is furtherconfigured to transmit K+1 NZP CSI-reference signals (RSs) over K+1 NZPCSI-RS resources configured by the signaling of the first NZP CSI-RSconfiguration and the second NZP CSI-RS configuration. In someembodiments, the processing circuitry is configured to signal to the UEby being further configured to signal semi-statically over radioresource control signaling. In some embodiments, the processingcircuitry is configured to send the CSI feedback request to the UE bybeing further configured to send the CSI feedback request dynamicallyover a downlink control channel. In some embodiments, the processingcircuitry is configured to signal to the UE by being further configuredto signal the second NZP CSI-RS configuration comprising a power scalingfactor for each of K NZP CSI-RS resources configured by the second NZPCSI-RS configuration for the interference measurement. In someembodiments, the received CSI report is based on a combined interferenceestimate and a measured downlink channel, the combined interferenceestimate being a sum of at least K interference power estimates based onK NZP CSI-RS resources configured by the second NZP CSI-RS configurationand at least one interference power estimate based on at least oneCSI-IM resource configured by the CSI-IM configuration, and the measureddownlink channel being based on a first NZP CSI-RS resourcecorresponding to the first NZP CSI-RS configuration. In someembodiments, the processing circuitry is further configured to send aCSI feedback request comprising a codebook configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of LTE physical resources;

FIG. 2 is a block diagram of the LTE time-domain structure;

FIG. 3 is a block diagram of transmission structure of precoded spatialmultiplexing mode in LTE;

FIG. 4 is a block diagram of REs available for CSI-RS allocation in eachPRB in LTE;

FIGS. 5 and 6 are block diagrams of an example of CSI-RS resource fortwo and four ports in LTE, respectively;

FIG. 7 is therefore a block diagram of NZP CSI-RS and ZP CSI-RSresources;

FIG. 8 is a block diagram of NZP CSI-RS, ZP CSI-RS and CSI-IM resources;

FIG. 9 is a block diagram of an exemplary system for interferencemeasurement and CSI feedback configuration for multi-user (MU)multiple-in multiple-out (MIMO) in accordance with the principles of thedisclosure;

FIG. 10 is a flow diagram of an exemplary configuration process ofconfiguration code in accordance with the principles of the disclosure;

FIG. 11 is a block diagram of three wireless devices that are MU-MIMOcandidates and each is configured with three NZP CSI-RS resources andone common CSI-IM resource;

FIG. 12 is a flow diagram of an exemplary estimation process ofestimation code in accordance with the principles of the disclosure;

FIG. 13 is a flow diagram of another embodiment of the configurationprocess of configuration code in accordance with the principles of thedisclosure;

FIG. 14 is a flow diagram of another embodiment of the estimationprocess of estimation code in accordance with the principles of thedisclosure;

FIG. 15 is a block diagram of method two in accordance with theprinciples of the disclosure;

FIG. 16 is an alternative embodiment of network node in accordance withthe principles of the disclosure; and

FIG. 17 is an alternative embodiment of wireless device in accordancewith the principals of the disclosure.

DETAILED DESCRIPTION

Note that although terminology from 3GPP LTE and NR (New Radio) may bebeen used in this disclosure to exemplify the embodiments in thedisclosure, this should not be seen as limiting the scope of thedisclosure to only the aforementioned systems. Other wireless systemsmay also benefit from exploiting the ideas covered within thisdisclosure.

Also note that terminology such as node, eNodeB/eNB/gNB and wirelessdevice/UE should be considering non-limiting and does in particular notimply a certain hierarchical relation between the two; in general,“eNodeB”/“node” could be considered as a first device and “UE”/“wirelessdevice” as a second device, and these two devices communicate with eachother over some radio channel. Herein, the focus will be on wirelesstransmissions in the downlink, but the disclosure is equally applicablein the uplink.

The methods and processes described herein are efficient forinterference measurement and CSI feedback for MU-MIMO. In one or moreembodiments, methods/processes described herein use K+1 NZP CSI-RSresources for K+1 wireless devices in MU-MIMO and one common ZP CSI-RSresource. Therefore, the methods and processes described herein may bescalable in the sense that only one more NZP CSI-RS resource may beneeded for each increased wireless device to participate in MU-MIMO. Theonce common ZP CSI-RS resource may still be used for each of theseincreased wireless devices.

In one or more embodiments, for a first method/process, other thaninterference estimation over additional NZP CSI-RS resources, theprocess may be similar for SU-MIMO CSI feedback such that minimal changemay be required at a wireless device.

In one or more embodiments, for a second method/process, precoding isalso taken into count in interference estimation due to network nodetransmission of emulated MU-MIMO interference and thus the interferenceestimation may be more accurate when compare to the first method.

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of components andprocessing steps related to methods, network nodes and wireless devices.Accordingly, components have been represented where appropriate byconventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments so as not toobscure the disclosure with details that will be readily apparent tothose of ordinary skill in the art having the benefit of the descriptionherein.

As used herein, relational terms, such as “first,” “second,” “top” and“bottom,” and the like, may be used solely to distinguish one entity orelement from another entity or element without necessarily requiring orimplying any physical or logical relationship or order between suchentities or elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the concepts described herein. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

In embodiments described herein, the joining term, “in communicationwith” and the like, may be used to indicate electrical or datacommunication, which may be accomplished by physical contact, induction,electromagnetic radiation, radio signaling, infrared signaling oroptical signaling, for example. One having ordinary skill in the artwill appreciate that multiple components may interoperate andmodifications and variations are possible of achieving the electricaland data communication.

Referring now to drawing figures in which like reference designatorsrefer to like elements there is shown in FIG. 9 is a block diagram of anexemplary system for interference measurement and CSI feedbackconfiguration for multi-user (MU) multiple-in multiple-out (MIMO) inaccordance with the principles of the disclosure. System 10 includes oneor more network nodes 12 and one or more wireless devices 14, incommunication with each other via one or more communication networks,paths and/or links using one or more communication protocols, asdescribed herein.

Network node 12 includes transmitter circuitry 16 and receiver circuitry18 for communicating with wireless device 14, other nodes 12 and/orother entities in system 10. In one or more embodiments, transceivercircuitry 16 and/or receiver circuitry 18 include and/or is/are replacedby one or more communication interfaces. Network node 12 includesprocessing circuitry 20. The term “network node”, such as “network node12” used herein can be any kind of network node comprised in a radionetwork which may further comprise any of base station (BS), radio basestation, base transceiver station (BTS), base station controller (BSC),radio network controller (RNC), evolved Node B (eNB or eNodeB), Node B,gNodeB (gNB), multi-standard radio (MSR) radio node such as MSR BS,relay node, donor node controlling relay, radio access point (AP),transmission points, transmission nodes, Remote Radio Unit (RRU) RemoteRadio Head (RRH), nodes in distributed antenna system (DAS) etc. Theterms “network node” and “base station” may be used hereininterchangeably.

Processing circuitry 20 includes processor 22 and memory 24. In additionto a traditional processor and memory, processing circuitry 20 maycomprise integrated circuitry for processing and/or control, e.g., oneor more processors and/or processor cores and/or FPGAs (FieldProgrammable Gate Array) and/or ASICs (Application Specific IntegratedCircuitry). Processor 22 may be configured to access (e.g., write toand/or reading from) memory 24, which may comprise any kind of volatileand/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM(Random Access Memory) and/or ROM (Read-Only Memory) and/or opticalmemory and/or EPROM (Erasable Programmable Read-Only Memory). Suchmemory 24 may be configured to store code executable by processor 22and/or other data, e.g., data pertaining to communication, e.g.,configuration and/or address data of nodes, etc.

Processing circuitry 20 may be configured to control any of the methodsand/or processes described herein and/or to cause such methods,signaling and/or processes to be performed, e.g., by network node 12.Processor 22 corresponds to one or more processors 22 for performingnetwork node 12 functions and processes described herein. Network node12 includes memory 24 that is configured to store data, programmaticsoftware code and/or other information described herein. In one or moreembodiments, memory 24 is configured to store configuration code 26. Forexample, configuration code 26 includes instructions that, when executedby processor 22, causes processor 22 to perform the functions describedherein such as the functions described with respect to FIGS. 10 and/or13.

Wireless device 14 includes transmitter circuitry 28 and receivercircuitry 30 for communicating with network node 12, other wirelessdevices 14 and/or other entities in system 10. In one or moreembodiments, transmitter circuitry 28 and/or receiver circuitry 30include and/or is/are replaced by one or more communication interfaces.Wireless device 14 includes processing circuitry 32.

Processing circuitry 32 includes processor 34 and memory 36. In additionto a traditional processor and memory, processing circuitry 32 mayinclude integrated circuitry for processing and/or control, e.g., one ormore processors and/or processor cores and/or FPGAs (Field ProgrammableGate Array) and/or ASICs (Application Specific Integrated Circuitry).Processor 34 may be configured to access (e.g., write to and/or readingfrom) memory 36, which may comprise any kind of volatile and/ornonvolatile memory, e.g., cache and/or buffer memory and/or RAM (RandomAccess Memory) and/or ROM (Read-Only Memory) and/or optical memoryand/or EPROM (Erasable Programmable Read-Only Memory). Such memory 36may be configured to store code executable by processor 34 and/or otherdata, e.g., data pertaining to communication, e.g., configuration and/oraddress data of nodes, etc.

Processing circuitry 32 may be configured to control any of the methodsand/or processes described herein and/or to cause such methods,signaling and/or processes to be performed, e.g., by wireless device 14.Processor 34 corresponds to one or more processors 34 for performingwireless device 14 functions and processes described herein. Wirelessdevice 14 includes memory 36 that is configured to store data,programmatic software code and/or other information described herein. Inone or more embodiments, memory 36 is configured to store estimationcode 38. For example, estimation code 38 includes instructions that,when executed by processor 34, causes processor 34 to perform thefunctions described herein such as the functions described with respectto FIGS. 12 and/or 15.

The terms “wireless device” and “UE” may be used herein interchangeably.Wireless device 14 may be a radio communication device, wireless deviceendpoint, mobile endpoint, device endpoint, sensor device, targetdevice, device-to-device wireless device, user equipment (UE), machinetype wireless device or wireless device capable of machine to machinecommunication, a sensor equipped with wireless device, tablet, mobileterminal, mobile telephone, laptop, computer, appliance, automobile,smart phone, laptop embedded equipped (LEE), laptop mounted equipment(LME), USB dongle and customer premises equipment (CPE), among otherdevices that can communicate radio or wireless signals as are known inthe art.

Although embodiments are described herein with reference to certainfunctions being performed by network node 12 and/or wireless device 14,it is understood that the functions can be performed in other networknodes and elements. It is also understood that the functions of thenetwork node 12 and/or wireless device 14 can be distributed across thenetwork cloud, such as the Internet or access network backhaul network,so that other nodes can perform one or more functions or even parts offunctions described herein.

In one or more embodiments, the configuration process at network node 12and the estimation process at each WD 14 are described below, accordingto a first exemplary aspect of the disclosure.

At network node 12

Step 1: Obtain SU-MIMO CSI;

Step 2: Determine K+1 WDs 14 as MU-MIMO candidates, configure eachcandidate with K+1 NZP CSI-RS resources and one CSI-IM resource;

Step 3: Indicate which NZP CSI-RS is for channel measurement;

Step 4: Request new CSI feedback with a codebook;

Step 5: Receive MU-MIMO CSI from each WD 14;

Step 6: Perform MU-MIMO transmission to the K+1 WDs 14 using the newCSIs.

At WD 14

Step 1: Receive configuration with K+1 NZP CSI-RS resources and oneCSI-IM and receive indication of one out of the K+1 NZP CSI-RS is forchannel measurement;

Step 2: Receive a CSI request from network node 12;

Step 3: Measure channel on the NZP CSI-RS resource as indicated;

Step 4: Measure inter-cell interference on CSI-IM

Step 5: Measure K MU interferences on the remaining K NZP CSI-RSresources, and subtract measured inter-cell interference from each ofthe K measured interferences, resulting in K MU interferences;

Step 6: Add the K MU-interferences and the measured inter-cellinterference, resulting in the total estimated interference;

Step 7: Calculate the CSI based on the measured channel and the totalestimated interference according to the configured codebook; and

Step 8: feedback the CSI (MU-MIMO CSI) to network node 12.

FIG. 10 is a flow diagram of an exemplary configuration process ofconfiguration code 26 of the network node 12 in accordance with theprinciples of the disclosure, and, in particular, in accordance with afirst exemplary aspect of the disclosure. Processing circuitry 20 ofnetwork node/base station 12 is configured to signal to a wirelessdevice/UE 14: a first Non-Zero Power (NZP) CSI-reference signal (RS)configuration for channel measurement; a second NZP CSI-RS configurationfor interference measurement; and a CSI interference measurement(CSI-IM) configuration for interference measurement (Block S100). Insome embodiments, the second NZP CSI-RS configuration is for multipleuser (MU) interference measurements on K NZP-CSI resources, where K>1.In some embodiments, the signaling includes a codebook configuration. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurements. In addition, the energy per RE ratio (EPRE) βbetween PDSCH and NZP CSI-RS for each NZP CSI-RS may also be signaled inthe first and second NZP CSI-RS configurations.

Processing circuitry 20 is optionally configured to send a CSI feedbackrequest to the wireless device 14 for CSI measurement and feedback basedon the first and second configurations NZP CSI-RS configurations for NZPCSI-RS resources and the CSI-IM configuration (Block S102). Processingcircuitry 20 is optionally configured to transmit K+1 NZP CSI-RS overthe configured K+1 NZP CSI-RS resources (Block S104). Processingcircuitry 20 is configured to receive a CSI report from the UE/wirelessdevice 14 (Block S106). In one embodiment, the CSI report is based atleast in part on the signaled first NZP CSI-RS configuration, the secondNZP CSI-RS configuration, and the CSI-IM configuration. In someembodiments, the CSI report is further based on the codebookconfiguration. Processing circuitry 20 is optionally configured totransmit data with the reported CSI to the wireless device 14 (BlockS108). In other words, in one or more embodiments of the configurationprocess, i.e., Method 1, network node 1 (e.g., network node 12) firstobtains SU-MIMO CSI (i.e. CRI, RI, PMI, CQI) from serving wirelessdevices 14 as is normally done in LTE or NR. Network node 12 thendetermines wireless device 14 candidates for MU-MIMO based on theSU-MIMO CSI. Assuming that K+1 wireless devices 14 are selected asMU-MIMO candidate, i.e., they can potentially be scheduled together in asubframe with the same time-frequency resources. To obtain MU-MIMO CQIby taking into account the MU interference, network node 12 configureseach of the K+1 wireless device 14 candidates with K+1 NZP CSI-RSresources and one common ZP CSI-RS as CSI-IM in the same subframe orslot and request CSI report from each wireless device 14.

For each wireless device 14, network node 12 also indicates one of theK+1 NZP CSI-RS resource for channel measurement and the remaining K NZPCSI-RS resources for interference measurements. Each wireless device 14is also configured with a codebook for CSI feedback.

After receiving the configuration and CSI feedback request, eachwireless device 14 estimates the downlink channel H and measuresinter-cell interference, I_(inter-cell) , over the ZP-CSI-RS resource.In addition, each wireless device 14 also measures MU-MIMO interference,I_(m) (m=1, . . . K), on each of the K NZP CSI-RS resources configuredfor interference measurement by assuming isotropical interference, i.e.,power averaging over all ports in a CSI-RS resource. The measurement canbe done over the whole bandwidth (i.e. wideband) and/or in each subband(i.e. over a number of PRBs). For example, assuming the CSI-IM consistsof four REs per PRB, then I_(inter-cell) and I_(m) for the kth wirelessdevice 14 at the ith PRB can be obtained as

${I_{{inter} - {cell}}^{k}(i)} = {\frac{1}{4}{\sum\limits_{l = 1}^{4}\; {{y_{ZP}^{k}\left( {n_{l},i} \right)}}^{2}}}$${I_{m}^{k}(i)} = {\sum\limits_{j = 1}^{N_{m}}\; {{y_{{NZP},m}^{k}\left( {n_{j},i} \right)}}^{2}}$

where y_(ZP) ^(k)(n_(l),i) is the received signal at the lth RE of theCSI-IM in the ith PRB and y_(NZP,m) ^(k)(n_(j), i) is the receivedsignal at the jth RE of mth NZP CSI-RS in the ith PRB, both at the kthUEWD 14. N_(m) is the number of CSI-RS ports of the mth NZP CSI-RSresource. While four REs are used for each CSI-IM in LTE, the number ofREs can be different in NR.

Each wireless device 14 estimates the total interference (i.e.,inter-cell plus MU interference) as I=Σ_(m=1)^(K)(I_(m)−I_(inter-cell))+I_(inter-cell) and calculates and reports CSIbased on I and H according to the configured codebook. That is, wirelessdevice 14 estimates interference I_(m) on each of the K NZP CSI-RSresources configured for interference measurement, removes the biasinter-cell interference I_(inter-cell) term from each interferenceestimate I_(m), and then sums the interference corresponding to the KNZP CSI-RS resources after removing the I_(inter-cell) bias to calculatethe total MU-interference (i.e., Σ_(m=1) ^(K)(I_(m)−I_(inter-cell))).

A difference from existing SU-MIMO CSI estimation may be that MUinterference is also estimated through the NZP CSI-RS configurations. Anexample is shown in FIG. 11, where three wireless devices 14 a-14 c areMU-MIMO candidates and each is configured with three NZP CSI-RSresources and one common CSI-IM resource. For wireless device 14 a,network node 12 indicates NZP CSI-RS1 for channel measurement. Forwireless device 14 b, NZP CSI-RS2 is indicated as for channelmeasurement and similarly for wireless device 14 c, NZP CSI-RS3 is forchannel measurement.

Although FIG. 10 illustrates an exemplary process including stepsS100-S108, it should be understood that some embodiments may includemore or less than the steps shown in FIG. 10 (e.g., only steps S100 andS106).

In an alternative embodiment, instead of including the measuredMU-interference from all the K NZP CSI-RS resources, network node 12 maysignal to wireless device 14 the interference hypotheses that wirelessdevice 14 should use to measure and report CSI. In one example, networknode 12 may ask wireless device 14 to report one SU-MIMO CSI byconsidering only the inter-cell interference, CSI0, one MU-MIMO CSIconsidering only the smallest measured MU-interference out of multipleMU interference estimates each measured on one of the K NZP CSI-RSresources, CSI1, and the associated NZP CSI-RS resource index, CRI1. Inthis case, wireless device 14 would report SU-MIMO CSI0, MU-MIMO CSI1and CRI1. This can help the network node 12 to decide which wirelessdevice 14 out of the K wireless devices 14 may be the best candidate forwireless device 14 to be paired with.

In another example, network node 12 may ask wireless device 14 to alsoreport an additional MU-MIMO CSI, CSI2, assuming wireless device 14 ispaired with another two wireless devices 14. In this case, the smallestsum MU-interference on any two NZP CSI-RS resources out of multiple MUinterference estimates is considered and the associated two NZP CSI-RSresource indices, CRI21 and CRI22, are also reported. Thus, the UE wouldreport SU-MIMO CSI0, MU-MIMO {CSI1, CR1}, {CSI2, CRI1, CRI22}. This canhelp network node 12 to decide which wireless device 14, or two wirelessdevices 14, out of the K wireless devices 14 may be the best candidatefor wireless device 14 to be paired with.

Similarly, the concept can be extended to interference hypotheses formore than two wireless devices 14.

FIG. 12 is a flow diagram of an exemplary estimation process ofestimation code 38 of wireless device 14 in accordance with theprinciples of the disclosure, and, in particular, in accordance with afirst exemplary aspect of the disclosure. Processing circuitry 32 isconfigured to receive signaling, the signaling including: a firstNon-Zero Power (NZP) CSI-reference signal (RS) configuration for channelmeasurement; a second NZP CSI-RS configuration for interferencemeasurements; and a CSI interference measurement (CSI-IM) configurationfor interference measurement (Block S110). In some embodiments, thesignaling further includes a codebook configuration. In someembodiments, the second NZP CSI-RS configuration is for multiple-user(MU) interference measurement. In some embodiments, the CSI IMconfiguration is for inter-cell interference measurement. Processingcircuitry 32 is optionally configured to receive a CSI feedback requestfor CSI based on the configured first and second configuration for NZPCSI-RS resources, and the CSI-IM configuration for the CSI-IM resource(Block S112). In some embodiments, the CSI feedback request for CSI isfurther based on the codebook configuration. Processing circuitry 32 isconfigured to estimate CSI based at least in part on the signaled firstNZP CSI-RS configuration, the second NZP CSI-RS configuration, and theCSI-IM configuration (Block S114). The first and second NZP CSI-RSconfigurations may be for the NZP CSI-RS resources, which may be K+1 NZPCSI-RS resources. In some embodiments, the processing circuitry 32 isfurther configured to estimate the CSI based on the codebookconfiguration.

Although FIG. 11 illustrates an exemplary process including stepsS110-S114, it should be understood that some embodiments may includemore or less than the steps shown in FIG. 11 (e.g., only steps S110 andS114).

In one or more other embodiments, the configuration process at networknode 12 and estimation process at each WD 14 are described below, inaccordance with a second exemplary aspect of the disclosure.

-   -   At network node 12:

Step 1: obtain SU-MIMO CSI for all WDs 14;

Step 2: determine K+1 WDs 14 as MU-MIMO candidates;

Step 3: configure each candidate with one NZP CSI-RS resource forchannel measurement and one CSI-IM resource for interferencemeasurement, including the power ratio parameter β;

Step 4: request a new CSI feedback with a codebook, and transmit aMU-MIMO signal over the CSI-IM resource;

Step 5: receive MU-MIMO CSI from each WD 14;

Step 6: perform MU-MIMO transmission to the K+1 WDs 14 using the newCSIs.

-   -   At WD 14:

Step 1: receive configuration with one NZP CSI-RS resource and oneCSI-IM resource, including the power ratio parameter β;

Step 2: receive CSI request and the codebook used for CSI feedback;

Step 3: measure the channel on the NZP CSI-RS resource and estimateprecoding matrix, and estimate signal power with the estimated precodingmatrix and the measured channel;

Step 4: measure interference on the CSI-IM resource and subtract theestimated signal power from the measured interference, resulting in thetotal estimated interference;

Step 5: calculate CSI based on the measured channel and the totalestimated interference according to the configured codebook;

Step 6: feedback the CSI (MU-MIMO CSI) to network node 12.

FIG. 13 is a flow diagram of another embodiment, i.e., method 2, of theconfiguration process of configuration code 26 of network node 12 inaccordance with the principles of the disclosure, and, in particular, inaccordance with the second exemplary aspect of the disclosure.Processing circuitry 20 of network node 12 is configured to signal to awireless device 14: a NZP CSI RS resource configuration for channelmeasurement; a CSI-IM resource configuration for interferencemeasurement; a codebook configuration (Block S116), and the power ratioβ. Processing circuitry 20 is configured to send a CSI feedback requestin a subframe or slot to wireless device 14 for CSI measurement andfeedback based on the configured NZP CSI-RS resource and the CSI-IMresource, the codebook (Block S118), and the power ratio β. Processingcircuitry 20 is configured to transmit a NZP CSI-RS signal over theconfigured NZP CSI-RS resource and a MU signal on the CSI-IM resources(Block S120). Processing circuitry 20 is configured receive a CSI reportfrom wireless device 14 (Block S122). In one embodiment, the CSI reportbeing based at least in part on the NZP CSI-RS resource configuration,the CSI-IM resource configuration, the codebook configuration and thepower ratio β. Processing circuitry 20 is configured to transmit datawith the reported CSI to wireless device 14 (Block S124).

FIG. 14 is a flow diagram of another embodiment of the estimationprocess of estimation code 38 of wireless device 14 in accordance withthe principles of the disclosure. Processing circuitry 32 of WD 14 isconfigured to receive: a NZP CSI RS resource configuration for channelmeasurement; a CSI-IM resource configuration for interferencemeasurement; a codebook configuration (Block S126), and a power ratio β.Processing circuitry 32 is configured to receive a CSI feedback requestin a subframe or slot for CSI measurement and feedback based on theconfigured NZP CSI-RS resource and the CSI-IM resource, the codebook(Block S128), and the power ratio β. Processing circuitry 32 isconfigured to receive a NZP CSI-RS signal over the configured NZP CSI-RSresource and a MU signal on the CSI-IM resources (Block S130).Processing circuitry 32 is configured to estimate CSI based on receivedsignals on the NZP CSI-RS resource and interference on the CSI-IMresource according to the codebook (Block S132) and the power ratio β.Processing circuitry 32 is configured to transmitting a CSI report(Block S134). The CSI report may be based on the estimated CSI.

Additional embodiments of a configuration process at network node 12 andestimation process at each wireless device 14 are described below.

In one or more embodiments of the configuration process, i.e., Method 2,similar to Method 1, it is assumed that network node 12 first obtainsSU-MIMO CSI (i.e. CRI, RI, PMI, CQI) from serving wireless devices 14 asis normally done in LTE or NR. Network node 12 then determines K+1 (K>0)wireless device 14 candidates for MU-MIMO based on the SU-MIMO CSI. Inthis method, to obtain MU-MIMO CQI by taking into MU interference,network node 12 configures each of the K+1 wireless device 14 candidateswith one NZP CSI-RS resource for channel measurement and one ZP CSI-RSas CSI-IM. The CSI-IM resource is common to the K+1 wireless devices 14in the same subframe or slot and request CSI report from each wirelessdevice 14.

Network node 12 transmits a MU-MIMO signal including all the K+1wireless devices 14 in the configured ZP CSI-RS resource, i.e. sendingthe following signals

Σ_(m=1) ^(K+1) W ^(m)(i)s ^(m)(i)

-   -   where W^(k)(i), s^(k)(i) are the precoding matrix and the data        vector associated with the kth UE at the i^(th) RE of CSI-IM        resource.

Each wireless device 14 measures interference, I_(ZP), over the CSI-IMresource and estimate a precoded signal power over the NZP CSI-RSresource, i.e. p_(s)=β∥HW∥̂2, where H is the estimated channel matrix andW is the estimated precoding matrix from the NZP CSI-RS resource. Eachwireless device 14 calculates and report CSI based on I=I_(ZP)−p_(s) andH according to the configured codebook. Here, the bias p_(s) is due tothe fact that a precoded signal intended for each wireless device 14 istransmitted in the CSI-IM resource for other wireless devices 14 in aMU-MIMO group to measure its interference. Thus, in one or moreembodiments, it is removed from the measurement I_(ZP) made on theCSI-IM resource to obtain an estimate of the total interference fromother wireless devices 14.

An example is shown in FIG. 15, where three wireless devices 14 a-14 care MU-MIMO candidates and each is configured with one NZP CSI-RSresource, i.e., NZP CSI-RS1 for wireless device 14 a, NZP CSI-RS 2 forwireless device 14 b, and NZP CSI-RS 3 for wireless device 14 c. Onecommon CSI-IM resource is also configured for all three wireless devices14.

FIG. 16 is an alternative embodiment of network node 12 in accordancewith the principles of the disclosure. In this embodiment, network node12 includes transmission module 40 for performing transmitting, sendingand/or signaling as described above. Network node 12 includesconfiguration module 42 for performing the functions and/or processes asdescribed above with respect to configuration code 26.

FIG. 17 is an alternative embodiment of wireless device 14 in accordancewith the principals of the disclosure. In this embodiment, wirelessdevice 14 includes receiving module 44 for receiving transmissions,communications and/or signaling from network node 12 as described above.Wireless device 14 includes estimation module 46 for performing theprocesses and/or functions describe above with respect to estimationcode 38.

According to one aspect of the disclosure, a method for a UE 14 isprovided. The method includes receiving (S110) signaling, by the UE 14,the signaling including: a first Non-Zero Power (NZP) channel stateinformation-reference signal (CSI-RS) configuration for channelmeasurement; a second NZP CSI-RS configuration for interferencemeasurement; and a CSI interference measurement (CSI-IM) configurationfor interference measurement; and estimating (S114), by the UE 14, CSIbased at least in part on the signaled first NZP CSI-RS configuration,the second NZP CSI-RS configuration, and the CSI-IM configuration.

According to this aspect, in some embodiments, second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments, the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the receiving (S110)signaling further includes receiving the signaling including a codebookconfiguration. In some embodiments, the estimating (S114) the CSIfurther comprises estimating the CSI based on the codebookconfiguration. In some embodiments, the method further comprisesreceiving (S112), by the UE 14, a CSI feedback request for CSI based onat least the first NZP CSI-RS configuration, the second NZP CSI-RSconfiguration, the CSI-IM configuration and the codebook configuration.In some embodiments, the method further comprises receiving (S112), bythe UE 14, a CSI feedback request for CSI based on at least the firstNZP CSI-RS configuration, the second NZP CSI-RS configuration, and theCSI-IM configuration. In some embodiments, the estimating (S114) the CSIfurther includes measuring a downlink channel on a first NZP CSI-RSresource corresponding to the first NZP CSI-RS configuration. In someembodiments, the estimating (S114) the CSI further includes measuringinterference on each of K NZP CSI-RS resources corresponding to thesecond NZP CSI-RS configuration. In some embodiments, the measuring theinterference on each of the K NZP CSI-RS resources results in Kinterference power estimates. In some embodiments, each of the Kinterference power estimates is scaled according to a power scalingfactor associated with the K NZP CSI-RS resources. In some embodiments,the second NZP CSI-RS configuration comprises a power scaling factor foreach of K NZP CSI-RS resources configured by the second NZP CSI-RSconfiguration for the interference measurement. In some embodiments, theestimating (S114) the CSI includes measuring interference on at leastone CSI-IM resource corresponding to the CSI-IM configuration. In someembodiments, the measuring the interference on the at least one CSI-IMresource results in at least one interference power estimate. In someembodiments, the method further comprises adding at least the Kinterference power estimates based on the K NZP CSI-RS resources and theat least one interference power estimate based on the at least oneCSI-IM resource to obtain a combined interference estimate. In someembodiments, the estimated CSI is based on the combined interferenceestimate and a measured downlink channel. In some embodiments, themeasured downlink channel is measured on a first NZP CSI-RS resourcecorresponding to the first NZP CSI-RS configuration. In someembodiments, the method further comprises receiving, by the UE 14, a CSIfeedback request comprising a codebook configuration.

According to another aspect of the disclosure, a UE 14 comprisingprocessing circuitry 32 is provided. The processing circuitry 32 isconfigured to cause the UE 14 to: receive signaling, the signalingincluding: a first Non-Zero Power (NZP) channel state information(CSI)-reference signal (RS) configuration for channel measurement; asecond NZP CSI-RS configuration for interference measurement; and a CSIinterference measurement (CSI-IM) configuration for interferencemeasurement; and estimate CSI based at least in part on the signaledfirst NZP CSI-RS configuration, the second NZP CSI-RS configuration, andthe CSI-IM configuration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>=1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments, the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the received signalingfurther includes a codebook configuration. In some embodiments, theprocessing circuitry 32 is configured to cause the UE 14 to estimate theCSI by being further configured to estimate the CSI based on thecodebook configuration. In some embodiments, the processing circuitry 32is further configured to cause the UE 14 to receive a CSI feedbackrequest for CSI based on at least the first NZP CSI-RS configuration,the second NZP CSI-RS configuration, the CSI-IM configuration and thecodebook configuration. In some embodiments, the processing circuitry 32is further configured to cause the UE 14 to receive a CSI feedbackrequest for CSI based on at least the first NZP CSI-RS configuration,the second NZP CSI-RS configuration, and the CSI-IM configuration. Insome embodiments, the processing circuitry 32 is configured to cause theUE 14 to estimate the CSI by being further configured to measure adownlink channel on a first NZP CSI-RS resource corresponding to thefirst NZP CSI-RS configuration. In some embodiments, the processingcircuitry 32 is configured to cause the UE 14 to estimate the CSI bybeing further configured to measure interference on each of K NZP CSI-RSresources corresponding to the second NZP CSI-RS configuration. In someembodiments, the processing circuitry 32 is configured to measure theinterference on each of the K NZP CSI-RS resources resulting in Kinterference power estimates. In some embodiments, the processingcircuitry 32 is configured to scale each of the K interference powerestimates according to a power scaling factor associated with the K NZPCSI-RS resources. In some embodiments, the second NZP CSI-RSconfiguration comprises a power scaling factor for each of K NZP CSI-RSresources configured by the second NZP CSI-RS configuration for theinterference measurement. In some embodiments, the processing circuitry32 is configured to cause the UE 14 to estimate the CSI by being furtherconfigured to measure interference on at least one CSI-IM resourcecorresponding to the CSI-IM configuration. In some embodiments, theprocessing circuitry 32 is configured to measure the interference on theat least one CSI-IM resource resulting in at least one interferencepower estimate. In some embodiments, the processing circuitry 32 isconfigured to cause the UE 14 to add at least the K interference powerestimates based on the K NZP CSI-RS resources and the at least oneinterference power estimate based on the at least one CSI-IM resource toobtain a combined interference estimate. In some embodiments, theprocessing circuitry 32 is configured to cause the UE 14 to estimate theCSI based on the combined interference estimate and a measured downlinkchannel. In some embodiments, the measured downlink channel is measuredon a first NZP CSI-RS resource corresponding to the first NZP CSI-RSconfiguration. In some embodiments, the processing circuitry 32 isfurther configured to cause the UE 14 to receive a CSI feedback requestcomprising a codebook configuration.

According to yet another aspect of the disclosure, a method for a basestation 12 is provided. The method includes signaling (S100), by thebase station 12, to a user equipment, UE 14: a first Non-Zero Power(NZP) channel state information (CSI)-reference signal (RS)configuration for channel measurement; a second NZP CSI-RS configurationfor interference measurement; and a CSI interference measurement(CSI-IM) configuration for interference measurement; and receiving(S106), by the base station 12, a CSI report from the UE 14, the CSIreport being based at least in part on the signaled first NZP CSI-RSconfiguration, the second NZP CSI-RS configuration, and the CSI-IMconfiguration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments, the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the signaling (S100)further includes signaling a codebook configuration. In someembodiments, the received CSI report is based at least in part on thesignaled codebook configuration. In some embodiments, the method furtherincludes sending (S102), from the base station 12, a CSI feedbackrequest to the UE 14 for CSI based on at least the first NZP CSI-RSconfiguration, the second NZP CSI-RS configuration, the CSI-IMconfiguration, and the codebook configuration. In some embodiments, themethod further includes sending (S102), from the base station 12, a CSIfeedback request to the UE 14 for CSI based on at least the first NZPCSI-RS configuration, the second NZP CSI-RS configuration and the CSI-IMconfiguration. In some embodiments, the method further includestransmitting (S104), from the base station 12, K+1 NZP CSI-referencesignals (RSs) over K+1 NZP CSI-RS resources configured by the signalingof the first NZP CSI-RS configuration and the second NZP CSI-RSconfiguration. In some embodiments, the signaling, by the base station12, to the UE 14 includes signaling semi-statically over radio resourcecontrol signaling. In some embodiments, the sending, from the basestation 12, the CSI feedback request to the UE 14 includes sending theCSI feedback request dynamically over a downlink control channel. Insome embodiments, the second NZP CSI-RS configuration comprises a powerscaling factor for each of K NZP CSI-RS resources configured by thesecond NZP CSI-RS configuration for the interference measurement. Insome embodiments, the received CSI report is based on a combinedinterference estimate and a measured downlink channel, the combinedinterference estimate being a sum of at least K interference powerestimates based on K NZP CSI-RS resources configured by the second NZPCSI-RS configuration and at least one interference power estimate basedon at least one CSI-IM resource configured by the CSI-IM configuration,and the measured downlink channel being based on a first NZP CSI-RSresource corresponding to the first NZP CSI-RS configuration. In someembodiments, the method further includes sending, from the base station12, a CSI feedback request comprising a codebook configuration.

According to yet another aspect of the disclosure, a base station 12comprising processing circuitry 20 is provided. The processing circuitry20 is configured to cause the base station 12 to: signal to a UE 14: afirst Non-Zero Power (NZP) channel state information (CSI)-referencesignal (RS) configuration for channel measurement; a second NZP CSI-RSconfiguration for interference measurement; and a CSI interferencemeasurement (CSI-IM) configuration for interference measurement; andreceive a CSI report from the UE 14, the CSI report being based at leastin part on the signaled first NZP CSI-RS configuration, the second NZPCSI-RS configuration, and the CSI-IM configuration.

According to this aspect, in some embodiments, the second NZP CSI-RSconfiguration is for configuring K NZP CSI-RS resources for theinterference measurement, where K>1. In some embodiments, theinterference measurement measured on the K NZP CSI-RS resourcescorresponds to multiple-user multiple-input multiple-output (MU-MIMO)interference. In some embodiments, K+1 corresponds to a number of userequipment candidates for multiple-user multiple-input multiple-output(MU-MIMO) communication. In some embodiments) the second NZP CSI-RSconfiguration is for multiple-user (MU) interference measurement. Insome embodiments, the CSI-IM configuration is for inter-cellinterference measurement. In some embodiments, the processing circuitry20 is configured to signal to the UE 14 by being further configured tosignal a codebook configuration. In some embodiments, the received CSIreport is based at least in part on the signaled codebook configuration.In some embodiments, the processing circuitry 20 is further configuredto send (S102) a CSI feedback request to the UE 14 for CSI based on atleast the first NZP CSI-RS configuration, the second NZP CSI-RSconfiguration, the CSI-IM configuration, and the codebook configuration.In some embodiments, the processing circuitry 20 is further configuredto send a CSI feedback request to the UE 14 for CSI based on at leastthe first NZP CSI-RS configuration, the second NZP CSI-RS configurationand the CSI-IM configuration. In some embodiments, the processingcircuitry 20 is further configured to transmit K+1 NZP CSI-referencesignals (RSs) over K+1 NZP CSI-RS resources configured by the signalingof the first NZP CSI-RS configuration and the second NZP CSI-RSconfiguration. In some embodiments, the processing circuitry 20 isconfigured to signal to the UE 14 by being further configured to signalsemi-statically over radio resource control signaling. In someembodiments, the processing circuitry 20 is configured to send the CSIfeedback request to the UE 14 by being further configured to send theCSI feedback request dynamically over a downlink control channel. Insome embodiments, the processing circuitry 20 is configured to signal tothe UE 14 by being further configured to signal the second NZP CSI-RSconfiguration comprising a power scaling factor for each of K NZP CSI-RSresources configured by the second NZP CSI-RS configuration for theinterference measurement. In some embodiments, the received CSI reportis based on a combined interference estimate and a measured downlinkchannel, the combined interference estimate being a sum of at least Kinterference power estimates based on K NZP CSI-RS resources configuredby the second NZP CSI-RS configuration and at least one interferencepower estimate based on at least one CSI-IM resource configured by theCSI-IM configuration, and the measured downlink channel being based on afirst NZP CSI-RS resource corresponding to the first NZP CSI-RSconfiguration. In some embodiments, the processing circuitry 20 isfurther configured to send a CSI feedback request comprising a codebookconfiguration.

Some embodiments of the disclosure include:

Embodiment 1. A method of channel state information feedback in awireless network consisting of access nodes equipped with multipletransmit antenna ports transmitting data to user equipments. The methodcomprises

Signaling, by a access node, to a UE a first NZP CSI-RS configurationfor channel measurement, and a second configuration for K>=1 NZP CSI-RSfor MU interference measurements, and a CSI-IM resource configurationfor inter-cell interference measurement, and a codebook configuration;and

Sending, by the access node, a CSI feedback request to the UE for CSImeasurement and feedback based on the configured the first and thesecond configuration for NZP CSI-RS resources, the CSI-IM resource, andthe codebook; and

Transmitting, from the access node, K+1 NZP CSI-RS over the configuredK+1 NZP CSI-RS resources; and

Estimating, by the UE, CSI based on the signaled first and the secondconfiguration of NZP CSI-RS resources, the CSI-IM resource, and thecodebook; and

Receiving, by the access node, a CSI report from the UE; and

Transmitting, from the access node, data with the reported CSI to theUE.

Embodiment 2. The method according to Embodiment 1, wherein theestimating comprises measuring downlink channel on the first NZP CSI-RSresource.

Embodiment 3. The method according to Embodiment 1, wherein theestimating further comprises measuring interference power on each of theK NZP CSI-RS resources, resulting in K interference power estimates.

Embodiment 4. The method according to Embodiment 1, wherein theestimating further comprises measuring an inter-cell interference poweron the CSI-IM resource;

Embodiment 5. The method according to Embodiment 3 and Embodiment 4,wherein the measured inter-cell interference power is subtracted fromeach of the K interference power estimates, resulting in K MUinterference power estimates.

Embodiment 6. The methods of Embodiment 3 to Embodiment 5, wherein the KMU interference power estimates and the inter-cell interference estimateare added up, resulting in a total interference estimate.

Embodiment 7. The methods of Embodiment 1 to Embodiment 6, wherein theCSI estimation is based on the total interference estimate and themeasured downlink channel.

Embodiment 7a. The method according to Embodiment 1, wherein the CSIfeedback request can further contain multiple interference hypotheses.

Embodiment 7b. The method according to Embodiment 7a, wherein theinterference hypothesis can include assumption of a number ofinterfering wireless devices or a maximum number of interfering wirelessdevices, each is associated with one of the K NZP CSI-RS.

Embodiment 7c. The method according to Embodiment 1, wherein the CSI canfurther contain a SU-MIMO CSI and one or more MU CSI.

Embodiment 7d. The method of Embodiment 7c, where the SU-MIMO CSIcorresponds to CSI without any MU interference.

Embodiment 7e. The method of Embodiment 7c, where the MU-MIMO CSIcorresponds to CSI with smallest sum MU interference estimated over anumber of NZP CSI-RS resources out of the K NZP CSI-RS resources;

Embodiment 7f. The method of Embodiment 7e, where the number of NZPCSI-RS resources is specified in the interference hypothesis.

Embodiment 8. The method according to Embodiment 1, wherein thesignaling is semi-static over radio resource control signaling.

Embodiment 9. The method according to Embodiment 1, wherein thesignaling is dynamic over downlink control channel.

Embodiment 10. The method according to Embodiment 1, wherein the sendingis dynamic over downlink control channel.

Embodiment 11. The method according to Embodiment 1, wherein thesignaling and the sending are in a same downlink control informationover downlink control channel.

Embodiment 11a. The method according to any one of Embodiments 1 to 11,wherein the first and the second NZP CSI-RS configurations furtherinclude a power ratio parameter for each NZP CSI-RS.

Embodiment 12. A method of channel state information feedback in awireless network consisting of access nodes equipped with multipletransmit antenna ports transmitting data to wireless devices, the methodcomprising:

Signaling, by an access node, to a wireless device, a NZP CSI-RSresource configuration for channel measurement, and a CSI-IM resourceconfiguration for interference measurement, and a codebookconfiguration; and

Sending, by the access node, a multi-user (MU) CSI feedback request in asubframe or slot to the wireless device for CSI measurement and feedbackbased on the configured NZP CSI-RS resource and the CSI-IM resource, andthe codebook; and

Transmitting, from the access node, a NZP CSI-RS signal over theconfigured NZP CSI-RS resource and a MU signal on the CSI-IM resource;and

estimating, by the UE, a MU CSI based on received signals on the NZPCSI-RS resource and interference on the CSI-IM resource according to thecodebook; and

Receiving, by the access node, a MU CSI report from the wireless device;and

Transmitting, from the access node, data with the reported CSI to theUE.

Embodiment 13a. The method according to Embodiment 12, wherein the NZPCSI-RS resource configuration for channel measurement further includes apower ratio parameter for each NZP CSI-RS.

Embodiment 13b. The method according to Embodiment 12, wherein theestimating comprises measuring downlink channel on the NZP CSI-RSresource.

Embodiment 14. The method according to any one of Embodiments 13b and13a, wherein the measuring further comprises measuring a precodingmatrix and a signal power by multiply the precoding matrix to theestimated channel and the power ratio.

Embodiment 15. The method according to Embodiment 12, wherein theestimating further comprises measuring interference power on the CSI-IMresource.

Embodiment 16. The method according to Embodiment 14 and Embodiment 15,wherein the measured signal power is subtracted from the measuredinterference power, resulting in a new estimate of interference power.

Embodiment 17. The method of Embodiment 12 to Embodiment 16, wherein theCSI estimation is based the new estimate of interference power and themeasured downlink channel.

Embodiment 18. The method according to Embodiment 1, wherein thesignaling is semi-static over radio resource control signaling.

Embodiment 19. The method according to Embodiment 1, wherein thesignaling is dynamic over downlink control channel.

Embodiment 20. The method according to Embodiment 1, wherein the sendingis dynamic over downlink control channel.

Embodiment 21a. The method according to Embodiment 1, wherein thesignaling and the sending are in a same downlink control informationover downlink control channel.

Embodiment 21b. The method according to any one of Embodiments 1 to 21a,wherein the NZP CSI-RS resource configuration for channel measurementincludes a power ratio parameter.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, the concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.”Furthermore, the disclosure may take the form of a computer programproduct on a tangible computer usable storage medium having computerprogram code embodied in the medium that can be executed by a computer.Any suitable tangible computer readable medium may be utilized includinghard disks, CD-ROMs, electronic storage devices, optical storagedevices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings withoutdeparting from the scope of the following claims.

What is claimed is:
 1. A method for a user equipment, UE, the methodcomprising: receiving signaling, by the UE, the signaling including: afirst Non-Zero Power, NZP, channel state information, CSI,-referencesignal, RS, configuration for channel measurement; a second NZP CSI-RSconfiguration for interference measurement; and a CSI interferencemeasurement, CSI-IM, configuration for interference measurement; andestimating, by the UE, CSI based at least in part on the signaled firstNZP CSI-RS configuration, the second NZP CSI-RS configuration, and theCSI-IM configuration.
 2. The method according to claim 1, wherein thesecond NZP CSI-RS configuration is for configuring K NZP CSI-RSresources for the interference measurement, where K>=1.
 3. The methodaccording to claim 1, wherein the estimating the CSI further includesmeasuring a downlink channel on a first NZP CSI-RS resourcecorresponding to the first NZP CSI-RS configuration.
 4. The methodaccording to claim 2, wherein the estimating the CSI further includesmeasuring interference on each of K NZP CSI-RS resources correspondingto the second NZP CSI-RS configuration.
 5. The method according to claim4, wherein the measuring the interference on each of the K NZP CSI-RSresources results in K interference power estimates.
 6. The methodaccording to claim 1, wherein the estimating the CSI includes measuringinterference on at least one CSI-IM resource corresponding to the CSI-IMconfiguration.
 7. The method according to claim 6, further comprisingadding at least the K interference power estimates based on the K NZPCSI-RS resources and the at least one interference power estimate basedon the at least one CSI-IM resource to obtain a combined interferenceestimate.
 8. The method according to claim 7, wherein the estimated CSIis based on the combined interference estimate and a measured downlinkchannel.
 9. A user equipment, UE, comprising processing circuitryconfigured to cause the UE to: receive signaling, the signalingincluding: a first Non-Zero Power, NZP, channel state information,CSI,-reference signal, RS, configuration for channel measurement; asecond NZP CSI-RS configuration for interference measurement; and a CSIinterference measurement, CSI-IM, configuration for interferencemeasurement; and estimate CSI based at least in part on the signaledfirst NZP CSI-RS configuration, the second NZP CSI-RS configuration, andthe CSI-IM configuration.
 10. The UE according to claim 9, wherein thesecond NZP CSI-RS configuration is for configuring K NZP CSI-RSresources for the interference measurement, where K>=1.
 11. The UEaccording to claim 9, wherein the processing circuitry is configured tocause the UE to estimate the CSI by being further configured to measurea downlink channel on a first NZP CSI-RS resource corresponding to thefirst NZP CSI-RS configuration.
 12. The UE according to claim 9, whereinthe processing circuitry is configured to cause the UE to estimate theCSI by being further configured to measure interference on each of K NZPCSI-RS resources corresponding to the second NZP CSI-RS configuration.13. The UE according to claim 12, wherein the processing circuitry isconfigured to measure the interference on each of the K NZP CSI-RSresources resulting in K interference power estimates.
 14. The UEaccording to claim 9, wherein the processing circuitry is configured tocause the UE to estimate the CSI by being further configured to measureinterference on at least one CSI-IM resource corresponding to the CSI-IMconfiguration.
 15. The UE according to claim 14, wherein the processingcircuitry is configured to cause the UE to add at least the Kinterference power estimates based on the K NZP CSI-RS resources and atleast one interference power estimate based on the at least one CSI-IMresource to obtain a combined interference estimate.
 16. The UEaccording to claim 15, wherein the processing circuitry is configured tocause the UE to estimate the CSI based on the combined interferenceestimate and a measured downlink channel.
 17. A base station comprisingprocessing circuitry, the processing circuitry configured to cause thebase station to: signal to a user equipment, UE: a first Non-Zero Power,NZP, channel state information, CSI,-reference signal, RS, configurationfor channel measurement; a second NZP CSI-RS configuration forinterference measurement; and a CSI interference measurement, CSI-IM,configuration for interference measurement; and receive a CSI reportfrom the UE, the CSI report being based at least in part on the signaledfirst NZP CSI-RS configuration, the second NZP CSI-RS configuration, andthe CSI-IM configuration.
 18. The base station according to claim 17,wherein the second NZP CSI-RS configuration is for configuring K NZPCSI-RS resources for the interference measurement, where K>=1.
 19. Thebase station according to claim 18, wherein the processing circuitry isfurther configured to transmit K+1 NZP CSI-reference signals, RSs, overK+1 NZP CSI-RS resources configured by the signaling of the first NZPCSI-RS configuration and the second NZP CSI-RS configuration.
 20. Thebase station according to claim 18, wherein the received CSI report isbased on a combined interference estimate and a measured downlinkchannel, the combined interference estimate being a sum of at least Kinterference power estimates based on K NZP CSI-RS resources configuredby the second NZP CSI-RS configuration and at least one interferencepower estimate based on at least one CSI-IM resource configured by theCSI-IM configuration, and the measured downlink channel being based on afirst NZP CSI-RS resource corresponding to the first NZP CSI-RSconfiguration.